They are just too boring and plain. Icons are meant to help you find the application easily. If you make them all the same with just a line of text in the middle, then that almost defeats the purpose for me.
But it is just a dock so I am not going to start an argument and go off topic with it, but icon mods arent for me (excluding changing the VLC icon, of corse).
I agree 100% i change my dock around a lot and at one point I found better alternatives to all the stock icons but then they just made the dock look awkward and i wasn't satisified with going back to the stock icons. So to answer ur question i like them because they made the dock look organized and non chaotic, clean, and simple. Kind of a minimalist approach